Hello!

While trying to make an animation out of some simulation results, I 
encountered a strange behaviour that makes the render time shoot up 
dramatically...

It seems that the bounding box optimization on some objects is turned on 
or off at the first frame only, and remains set for the subsequent 
frames. Example files:

// animbug.pov //////////////////////////////
camera{location 0 look_at x}
light_source{10000 color rgb 1}

#declare i = 0;
#while(i<clock)
     sphere{i*x - y, 0.1 pigment{rgb 1}}
     #declare i = i+1;
#end
////////////////////////////////////////////

;; animbug.ini ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Input_File_Name = "animbug.pov"
Initial_Frame = 1
Final_Frame = 80
Initial_Clock = 1
Final_Clock = 80
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

If the render is launched with the command:
$ povray animbug

it takes a long time and if you look at the output, bounding boxes are 
never used to speed-up intersection tests.

On the other hand:
$ povray animbug +MB1

renders faster and uses bounding boxes.

More generally it seems that if the number of objects on the first frame 
does not exceed the bounding threshold the optimization is never used, 
even if there are more objects in the rest of the frames.

Is this the expected behaviour? Am I the only one starting with just 1 
object in the first frame :-) ?

Regards,

-- 
Vincent

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I have found a reference to the same behaviour in this message :

http://news.povray.org/povray.advanced-users/message/%3C47d3f0df%241%40news.povray.org%3E/#%3C47d3f0df%241%40news.povray.org%3E

Chris B wrote:
> I vaguely recall a discussion about starting an animation with no objects in 
> the first frame a while ago and reading that POV-Ray makes some assumptions 
> (maybe about bounding/vista buffering, I can't remember exactly) and that 
> the assumption then lasts for the entire animation sequence. If memory 
> serves me correctly I think the conclusion of that discussion was that it 
> was more a 'feature' than a 'bug'.

Alas I have been unable to find the discussion in question... Anyone 
remembers how it is more a 'feature' than a 'bug'?

-- 
Vincent

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Vincent Le Chevalier <gal### [at] libertyALLsurfSPAMfr> wrote:

>
> More generally it seems that if the number of objects on the first frame
> does not exceed the bounding threshold the optimization is never used,
> even if there are more objects in the rest of the frames.
>
> Is this the expected behaviour? Am I the only one starting with just 1
> object in the first frame :-) ?
>

I'm rather new to POV animation, so this is some interesting info. Thanks also
for the link to the other post. I've had to deal with Bounding_Threshold
problems too, not in animation, but in certain scenes using media. Still don't
understand that behavior.

BTW, I've found that the default Bounding_Threshold in v3.6.1c is 3, not 25 as
mentioned in the docs.

I just tried an animation experiment (of a scene with about 10 objects in it),
and set the Bounding_Threshold to first 100 (basically to turn it off) and then
to 0 (so that it's always on, AFAIK.)  There's definitely an overall major
render-time decrease when using 0--or whatever value that's <= the number of
objects in the scene. (A nice discovery for me, which I didn't know about until
now.) Using +MB0 may be the answer to your own problem--so that even with only
one (or no!) objects in the scene, automatic bounding will still kick in for
the rest of the animation.

Ken W.

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